Method of manufacturing electric conductor insulated by foamed crystalline polymer



y 1970, CHISATO KAWAZOE ET A METHOD OF MANUFACTURING ELECTRIC CONDUCTOR INSULATED BY FOAMED CRYSTALLINE POLYMER Filed May 31. 1966 ,4 mm 6 mm w Nl EHH T v: 0 7 N10 2 3 v e MQ RQ W 8 s a .K w w 0mm m m M c a 9 m :5 .WQQS

Tl-lelzArmeuevs United States Patent Office Patented July 21, 1970 METHOD OF MANUFACTURING ELECTRIC CON- DUCTOR INSULATED BY FOAMED CRYSTAL- LINE POLYMER Chisato Kawazoe, Tokyo-to, Terumichi Ichiba, Kamakurashi, and Seichi Iwakura and Hiroshi Shimba, Yokohama-shi, Japan, assignors to Sumitomo'Electric Industries, Ltd., Osaka, Japan, a company of Japan Filed May 31, 1966, Ser. No. 554,146 Claims priority, application Japan, June 1, 1965, 40/32,588, 40/312,589 Int. Cl. B44d 1/42 US. Cl. 117232 4 Claims ABSTRACT OF THE DISCLOSURE A method of accelerating the clouding phenomenon of a heated crystalline polymer solution coating on a conductor preliminary to foaming the conductor by the application of heat wherein the coated conductor is passed through water heated at a temperature of at least 50 C. to accelerate the separation of aggregated polymer particles in the coating. The coated conductor is thereafter dried to remove the polymer solvent remaining on the coating surface and in the interstices among the aggregated polymer particles. An-additional step to be executed just prior to drying may be added whereby either air is blown at a temperature of at least 35 C. onto the coated conductor or it is passed through a liquid which is compatible with the solvent.

The present invention relates to an improvement in the method of manufacturing foamed plastic insulated electric conductors by applying a high-temperature viscous solu tion of crystalline polymer, e.g. polyethylene, polypropylene, etc., over an electric conductor and making closed cells in the interior of the coating.

The conventional method illustrated in the blockdiagram of FIGLI andemployedfor the manufacture of foamed plastic insulated electric conductors is such that asolution of crystalline polymer, e.g. polyethylene, polypropylene, etc., is coated over the conductor w in a solution coating tank 1. Then the coated conductor passes through a drying duct 3 for drying, after which it is passed through a foaming furnace (or heating furnace) 4 to produce closed cells in the interior of coating. The foamed plastic insulated electric conductor thus obtained is taken up on reel 5. 1

. -When the conductor w coated with the solution 2 has entered the drying duct 3, both cooling of the coated solution and evaporation of the solvent in the coated Solution are simultaneously commenced. Thereafter, most of the solvent is separated from the coated solution and polyethylene containing the remaining solvent is coagulated by cooling, and then nearly spherically aggregated polymer particles with interstices among them are grown in the coating. The coating comes to appear white at this moment and this phenomenon is therefore referred to as clouding (or whitening).

The coated conductor whose coating has become white, then enters the foaming furnace 4 where closed cells are produced in the coating due to the re-melting of the polyethylene and the vaporization of the remaining solvent by heating to obtain a foamed insulated conductor.

However, when the aboveementioned method is appolymer used. Furthermore, as the method does not provide any means to accelerate the clouding phenomenon, the time required for the occurrence of the clouding phenomenon is excessive and consequently the coating line speed is restricted within a lower range. a

An object of the present invention is to increase the line speed of the coating process and to make it independent of changes in the atmospheric conditions. More particularly, the object is to accelerate the clouding phenomenon which is a prerequisite for foaming of the coatmg.

The first feature of the present invention is that a solution of crystalline polymer is coated over a conductor and the coated conductor thus obtained is then dipped in warm water, followed by drying and subsequent heating to produce closed cells in the coating.

The second feature of the present invention is that a solution of crystalline polymer is coated over a conductor and the coated conductor thus obtained is then dipped in warm water, and warm air is then blown onto the surface of the coated conductor, followed by drying and subsequent heating to produce closed cells in the coating.

The third feature of the present invention is that a solution of crystalline polymer is coated over a conductor and the coated conductor thus obtained is dipped in Warm water and is then dipped in a liquid which is compatible with the solvent of said solution, followed by drying and subsequent heating to produce closed cells in the coating.

Other objects and advantages appear hereinafter in the following description and claims.

The accompanying drawings show, for the purpose of exemplification without limiting the invention or the claims thereto, certain practical embodiments illustrating the principles of this invention wherein:

FIGS. 2 to 4 are block diagrams showing the respective features of the manufacturing method of the present invention, FIG. 2 showing the first aforementioned feature of the present invention, FIG. 3 the second feature and FIG. 4 the third feature. In all of the figures, the same numerals or letters as used in FIG. 1 represent the same parts, devices, or materials.

In FIG. 2, 1 denotes the solution coating'tank, 2 denotes the solution of crystalline polymer, e.g. polyethylene, polypropylene, etc., 3 the drying duct, 4 the foaming or heating furnace, and 5 the take-up reel, just as in FIG. 1, except that a hot water trough .11 is provided next to the solution coating tank 1.

The conductor w over which the solution 2 of crystalline polymer has been employed, first enters the hot water trough 11 and then the coating is dried in the drying duct 3 in the same way as before. It is then heated in the same way as before. It is thereafter heated in the foaming furnace 4-to produce closed cells in the coating and wound up on the take-up reel 5. i

If the conductor coated with the solution of crystalline polymer is dipped in warm water as mentioned, the coating is rapidly cooled below its solidifying temperature and the interior of the coating acquires a condition under which the-aggregated particles of the polymer are easily separated from the coated solution, so that the time required for the occurrence of the clouding may be'reduced remarkably.

As a result of various repeated experiments, it has been found that the suitable temperature of the warm water is 50 C. or higher, the optimum temperature being 65 to C. The suitable duration of immersion is- 0.05 to 10 seconds. On the other hand, if the temperature of warm water is lower than 50 C., the clouding phenomenon is not sufficiently accelerated such that the object of the present invention will be fully attained. Furthermore, the dipping of the coated conductor in warm water is also 3 effective to prevent the vibration of the coated conductor due to the damping effect of water.

FIG. 3 is a block diagram showing the second feature of the present invention. After the coated conductor is dipped in the hot water trough 11 as shown in FIG. 2, it passes through a hot air blow duct 12 before it is subjected to drying and heating for foaming and is taken up on a reel. In this example of embodiment, the clouding phenomenon is more accelerated than in the example of the embodiment shown in FIG. 2. If the conductor coated with a solution of crystalline polymer passes through-the hot water trough 11 as shown in FIG. 2, the seperation of aggregated polymer particles is accelerated but the solvent in the coating may not yet be evaporated sufiiciently, part of the solvent still remains on the surface of the coating and in the interstices among the aggregated polymer particles. Such residual solvent can be forcibly evaporated by passing the coated conductor through the hot air blow duct 12 and consequently the clouding phenomenon is further accelerated.

As the first example of this invention, a 28 wt. percent xylene solution of high density polyethylene which was kept at approximately 130 C. was coated over a 0.32 mm. copper conductor, and the coated conductor was dipped in 75 C. water for seconds. Samples prepared in this way and samples treated by air-blowing with an air temperature of 60 C. and at an air velocity of 1 m./sec. after the above-mentioned dipping were compared with samples made by the conventional method by measuring the time required for the occurrence of the clouding. The diameter of all of the coated conductor samples was controlled '(to approximately 0.55 mm.) so as to prevent the effect of the thickness variation of the coating on the above-mentioned comparison. The results, which are given below, confirm that the object aimed at is attained.

Clouding time in seconds.(Clouding time expressed in seconds means the time measured from the moment the sample left the solution coating tank to the moment the clouding phenomenon occured.)

60 C. air-blow- As a result of various experiments, it has been found that the suitable air temperature for blowing is 35 C. or higher, the optimum temperature being 45 to 65 C.

FIG. 4 is a block diagram showing the third feature of the present invention. As in FIGS. 2 and 3, 11 denotes a hot water trough. 13 denotes a tank containing a liquid which is compatible with the solvent used for the solution of crystalline polymer. As done before, the conductor coated with a solution of crystalline polymer is first dipped in the hot water trough 11. It is then dipped in the liquid tank 13 and subsequently dried in the drying duct 3, heated in the foaming furnace 4 for complete foaming of the coating and therafter taken-up on the reel 5 just as done before.

As already mentioned, the dipping of the conductor coated with a solution in warm water accelerates the clouding phenomenon. However, if the coated conductor passes through the hot water trough 11 only, the solvent does not evaporate sufficiently but partly remains on the surface of coating and in the interstices among the aggregated polymer particles. Such remaining traces of the solvent is forcibly dissolvedand extracted by passing through the liquid tank 13 and the clouding phenomenon is accelerated further. As a liquid for this purpose, alkyl alcohols, chlorinated hydrocarbons, aromatic hydrocarbons, etc. may be used for a xylene solution of crystalline polymer for example and the temperature of the liquid may be at room temperature, though it is preferable to make it 50 C. or higher.

As the second example of this invention, a 28% xylene solution of high density polyethylene which was kept at approximately 130 C. was coated over a 0 .32 mm. copper conductor, and then the coated conductor was dipped in 75 C. water for 3 seconds immediately after coating, and then dipped in N-propanol of 53 C. for 2 seconds, and some for 4 seconds. Then the clouding time of these samples as well as of samples made by the conventional method was measured in accordance with the same method as used in the first example. The diameter of all of the coated conductor samples was controlled to approximately 0.55 mm. so as to prevent the effect of the thickness variation of the coating on the above-mentioned comparison. As against to 27 seconds for thesamples by the conventional method, the

time required for these samples was reduced to 9 seconds and 10 seconds respectively.

As stated above, the manufacturing method of the present invention accelerates forcibly the clouding phenomenon, which is a prerequisite to foaming of the coating by dipping in warm water, or by dipping in warm water and warm air blowing, or by dipping in warm water and in a liquid solution compatible with the polymer solvent. The manufacturing speed is increased Without being affected to any noticeable extent by the kind of polymer used. Production speed can be maintained year round without being affected by the changes in atmospheric conditions;

What we claim is:

1. Av method of manufacturing a foamed plastic insulated electric conductor comprising th steps of coating a conductor with a solvent solution of crystalline polymer, dipping the coated conductor for a duration of 0.05 to 10 seconds in warm water heated in the range of 50 C. to C. to effect clouding of the coating, drying the dipped coated conductor and thereafter heating the same to-produce closed cells in the coating.

2. A method of manufacturing a foamed plastic insulated electric conductor as claimed in claim 1 which is characterized in that after dipping the coated conductor in warm water, wann air heated in the range of 35 C. to 65 C. is blown onto the surface of the coated conductor to remove solvent in the coating with subsequent drying and heating to produce the closed cells in the coating.

3. A method of manufacturing a foamed plastic insulated electric conductor as claimed in claim 1, which is characterized in that after dipping in warm water, the coated conductor is dipped in a liquid which is compatible with the solvent used for the solution of crystalline polymer, with subsequent drying and heating to produce closed cells in the coating.

4. A method of manufacturing a foamed plastic insulated electric conductor as claimed in claim 1, which is characterized in that after dipping in warm water, the coated conductor is dipped in N-propanol of at least 50 C. temperature, with subsequent drying and heating to produce closed cells in the coating.

References Cited UNITED STATES PATENTS 3,170,968 2/1965 Rokunohe et al. 117-232 2,930,718 3/1960 Abbott 117-232 3,017,371 1/1962 Hohenberg et al. 117232 3,068,126 12/1962 Rokunohe et al. 117232 MURRAY KATZ, Primary Examiner R. M. SPEER, Assistant Examiner US. Cl. X.R. 11762.2, 63 

